The maximum sentence a judge can impose on a defendant convicted of perverting the course of justice is life imprisonment. It is a common law offence that must be tried before a jury in a crown court.

But the average sentence served by those jailed for the offence, according to Ministry of Justice figures from December 2010, is 10 months. Curiously, the average for women, at 12.3 months, is higher than for men (9.6 months).

A 2007 appeal judgment said that appropriate sentences for perverting the course of justice should depend on three factors – the "seriousness of the substantive offence to which the perverting of the course of justice related, the degree of persistence, and the effect of the attempt to pervert the course of justice on the course of justice itself".

According to Archbold, the criminal lawyers' reference book, the normal range in sentencing those guilty of concealing evidence is four to 18 months – though longer in more serious cases.

Jeffrey Archer was sentenced to four years' jail in 2001 and perverting the course of justice by concealing the existence of a diary. He was also imprisoned for several offences of perjury.

Rebekah and Charlie Brooks and their co-accused will first appear at Westminster magistrates court on 13 June. There are likely to be a series of hearings before a date is fixed for the full crown court trial.

That may well not start before next year. The more complex the trial, the longer it will require, usually resulting in cases being scheduled further ahead when a long period of court time remains unallocated to other hearings.